Pile hammers have been manufactured for well over one hundred years. One early model of a very similar pile hammer is still manufactured by the company which currently manufactures and markets the hammer produced by the company which obtained that patent in the late 1800's. As one might imagine, various improvements occurred to the basic pile hammer design over the years.
Many pile hammers rely on an external source of compressed air, steam, hydraulic fluid or rope release. Some hammers are single acting air/steam hammers. These are the oldest mechanically powered hammer types. A ram is moved upward by compressed air or steam in a cylinder acting against a piston. Prior to reaching the rated stroke position the pressure under the piston is released and the ram first coasts on to the rated stroke and then falls under the influence of gravity. Just before hitting the bottom, pressure is again allowed to enter the cylinder.
In an effort to make pile hammers faster, air or steam pressure can be applied to the ram during its descent. These are called double or differential acting air/steam hammers. These designs may allow for shorter stroke to achieve a comparable energy rating to single acting hammers. However, this type hammer is more complex and timing issues are more critical than for the single acting hammers. Also, in hard driving, the hammers can experience upflips (the pile and thus the ram rebound too strongly) and the operator may be forced to reduce the pressure and thus the energy of the hammer. For these reasons, these style hammers are typically given a hammer efficiency of 50%.
Vulcan Iron Works, Inc. manufactured two prototype designs of a different type of hammer in the early 1980's. The “Model 300” was tested in 1982 and the SC3 which was apparently developed in late 1981 and then tested in the spring of 1983. Unfortunately, the Model 300 and/or SC3 prototypes probably do not qualify as “experimental use” even though this design has not been in use for over thirty years. Apparently the SC3 design was tested twice on projects in west Tennessee in late summer of 1983. Although the tests were deemed to be successful, the impact velocity of the ram was determined to be deficient due to the positioning of the ports which tended to reduce the impact velocity of the ram.
The Model 300 and the SC3 had a piston type ram with slots extending longitudinally on the ram which admitted air both just before and just after impact. These slots directed the fluid to enter the ram cylinder and internally. The compressed air pushed the ram upward until the exhaust ports were encumbered. The ram then proceeded upwardly to the top of the stroke, falling again to impact (under the influence of gravity) while compressing the air again during the down stroke to impact the anvil once again. This step made the process “one ended” and produced a hammer so that the ram would be thrown upwards and allowed it to fall downward and impact the pile with a solid anvil compressing the air after it passed the exhaust ports. The SC3 design was also a two-piece cylinder design having two different diameters which was difficult to assemble and run together due to the tolerances required by the construction. It provided a square reservoir that tended to bulge during pressurization. Furthermore, the exhaust was at the top and the piston had a larger diameter cylinder than the ram.
Additionally, this hammer did not have a stroke control feature, and, in fact, the hammer was prone to air locking which required disassembly to reset due possibly to insufficient air reservoir space. Another design defect included inadvertent starting, a significant safety concern which could also have been due to insufficient air reservoir space. When the offshore market collapsed in the early 1980's with oil prices, Vulcan decided not to commercialize the product and abandoned the project.
Accordingly, after almost thirty years, the applicant has decided to resurrect portions of the abandoned design as well as improve its observed deficiencies in an effort to provide an improved pile hammer construction to overcome defects that contributed to its abandonment by earlier efforts.